Golf ball

ABSTRACT

A one-piece solid golf ball including a matrix containing one or more rubber components in which butadiene rubber is a predominant component, and pulverized rubber obtained by pulverizing a one-piece solid golf ball predominantly containing butadiene rubber, wherein the pulverized rubber is incorporated in amount of 1-30 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix. Also disclosed is a multi-piece golf ball including a core and one or more cover layers, the core including a matrix and pulverized rubber obtained by pulverizing a one-piece solid golf ball, the matrix containing one or more rubber components, wherein the pulverized rubber is incorporated in amount of 1-30 parts by mass on the basis of 100 parts by mass of the rubber components of the matrix.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a one-piece solid golf ball anda multi-piece solid golf ball which have suppressed restitution andattain a short carrying distance, making them suitable for use on golfpractice ranges.

[0003] 2. Description of the Related Art

[0004] In many cases, one-piece solid golf balls (hereinafter may bereferred to as simply “one-piece balls”) are used on golf practiceranges (hereinafter the expression “balls used on golf practice ranges”will be simplified to “practice golf balls”), although the golf ballsmay be used as course balls (i.e., balls used on golf courses). InJapan, where most golf practice ranges are small, one-piece balls aredesigned so as to attain a short carrying distance and have durabilityagainst repeated hitting in view of production costs. Customary practicegolf balls are designed so as to have a hardness slightly higher thanthat of course balls (i.e., balls used on golf courses).

[0005] In recent years, the carrying distance of golf balls has beenincreased considerably in association with improvement of golf clubs. Asa result, in Japan, where most golf practice ranges are small, therearises the problem that hit golf balls tend to fly outside the practiceranges. Therefore, demand has increased for one-piece balls ofsuppressed restitution and short carrying distance which are suited foruse as practice golf balls.

[0006] In connection with this demand, conventionally, there has beendisclosed a one-piece ball of short carrying distance, which containsbase rubber (100 parts by weight) and acrylonitrile-butadiene rubber(3-40 parts by weight) (Japanese Patent Application Laid-Open (kokal)No. 7-24087).

[0007] However, the one-piece ball disclosed in Japanese PatentApplication Laid-Open (kokai) No. 7-24087 involves a problem in terms ofproduction.

[0008] Specifically, since rubber materials having different propertiesmust be kneaded during the production process, a method for feeding thematerials during the kneading step must be controlled and an optimumkneading temperature must be determined, rendering the overallproduction techniques complicated.

[0009] Meanwhile, among golf practice range owners, there has beendemand for use of multi-piece golf balls, such as two-piece solid golfballs and three-piece solid golf balls, which are used on golf courses,so as to distinguish their businesses from other golf practice ranges.

[0010] From golfers' viewpoints, golfers have complained aboutconventional practice golf balls, in that they cannot acquire a distancesensation regardless of how much they practice with the practice balls,due to the difference in carrying distance between the practice ballsand course balls. Also, golfers complain that they cannot practice in aneffective way with customary practice golf balls, because of thedifference in ball trajectory for an approach shot (shot angle; i.e.,the height of shot ball) between the practice balls and course balls,the difference being attributed to the difference in hardness betweenthe practice balls and course balls.

[0011] However, conventional multi-piece golf balls cannot be used aspractice golf balls, since the balls have a very long carrying distance,and they may fly outside golf practice ranges upon being hit. Forexample, when a conventional practice one-piece golf ball is shot at1,376 rpm, the initial velocity of the ball is about 74 m/s as measuredby use of a USGA-type initial velocity meter, whereas when acommercially available multi-piece golf ball is shot at 1,376 rpm, theinitial velocity of the ball is about 77 m/s as measured by use of themeter. When the difference in carrying distance between the one-piecegolf ball and the multi-piece golf ball is estimated on the sole basisof the difference in initial velocity; i.e., when differences attributedto dimples and other factors are neglected, the difference in carryingdistance is about 20-30m.

[0012] Therefore, in order to realize multi-piece golf balls which aresuitable as practice golf balls, the carrying distance of themulti-piece balls must be reduced. However, in view that conventionalmulti-piece golf balls—having a core coated with one or more covers—havebeen developed as course balls so as to increase the carrying distance,no practical means have ever been proposed for realizing use of suchmulti-piece golf balls as practice golf balls of short carrying distanceand low cost.

SUMMARY OF THE INVENTION

[0013] In view of the foregoing, a first object of the present inventionis to provide, through a simple production process, a one-piece ball ofsuppressed restitution so as to attain a short carrying distance.

[0014] A second object of the present invention is to provide amulti-piece golf ball of low restitution so as to attain a shortcarrying distance.

[0015] In order to achieve the first object, the present inventors haveperformed extensive studies, and have found that when a one-piece ballpredominantly containing butadiene rubber contains a pulverized productof a similar one-piece ball in a predetermined amount, the resilience ofthe one-piece ball is reduced, the initial velocity of the ball uponbeing hit is lowered appropriately, and the carrying distance of theball is reduced.

[0016] The present invention has been accomplished on the basis of theabove findings. Accordingly, in a first aspect of the present invention,there is provided a one-piece solid golf ball comprising a matrixcontaining one or more rubber components in which butadiene rubber is apredominant component, and pulverized rubber obtained by pulverizing aone-piece solid golf ball predominantly containing butadiene rubber,wherein the pulverized rubber is incorporated in an amount of 1-30 partsby mass on the basis of 100 parts by mass of the rubber components ofthe matrix.

[0017] In order to achieve the second object, the present inventors haveperformed extensive studies, and have found that when a multi-piece golfball containing a core and one or more cover layers contains apredetermined amount of a pulverized one-piece ball in the matrix of thecore, the resilience of the multi-piece ball is reduced, the initialvelocity of the ball upon being hit is appropriately lowered, and thecarrying distance of the ball is reduced.

[0018] The present invention has been accomplished on the basis of theabove findings. Accordingly, in a second aspect of the presentinvention, there is provided a multi-piece golf ball comprising a coreand one or more cover layers, the core comprising a matrix andpulverized rubber obtained by pulverizing a one-piece solid golf ball,the matrix containing one or more rubber components, wherein thepulverized rubber is incorporated in an amount of 1-30 parts by mass onthe basis of 100 parts by mass of the rubber components of the matrix.

DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

[0019] The present invention will next be described in detail. In thefirst aspect of the present invention, pulverized rubber obtained bypulverizing a one-piece ball predominantly containing butadiene rubberis incorporated into the matrix of a one-piece ball predominantlycontaining butadiene rubber.

[0020] Typical examples of the butadiene rubber include1,4-cis-polybutadiene. As used in connection with the first aspect ofthe present invention, the term “matrix” refers to a rubber compositionserving as a rubber base material of the one-piece ball.

[0021] In the second aspect of the present invention, pulverized rubberobtained by pulverizing a one-piece ball is incorporated into the matrixof the core of a multi-piece golf ball. As used in connection with thesecond aspect of the present invention, the term “matrix” refers to arubber composition serving as a rubber base material of the core.Examples of the matrix of the core of the multi-piece golf ball includea composition predominantly containing butadiene rubber, such as1,4-cis-polybutadiene, which is cross-linked by a cross-linking agentpredominantly containing zinc acrylate. Examples of the one-piece ballfrom which the pulverized rubber is obtained include a one-piece ballpredominantly containing butadiene rubber, such as1,4-cis-polybutadiene, which is cross-linked by a cross-linking agentpredominantly containing methacrylic acid and zinc.

[0022] In the first and second aspects of the present invention,preferably, the pulverized rubber is prepared so as to contain rubberparticles having an average size of more than 0.80 mm in an amount ofabout 30%, and rubber particles having an average size of 0.80 mm orless in an amount of about 70%. The average particle size is determinedby averaging the diameters of 100 rubber particles which are randomlyselected from the pulverized rubber particles, each particle beingregarded as a sphere.

[0023] The pulverized rubber may be obtained by pulverizing a one-pieceball after the surface coating of the ball is removed, or may beobtained by pulverizing a one-piece ball having a surface coating. Inthe latter case, a step of removing the surface coating can be omittedduring production of the pulverized rubber. In general, surface coatingof a one-piece ball is performed as follows: the surface of the ball iscovered with white coating after the ball is formed throughvulcanization; a marking for discernment (e.g., brand name or logo) isprinted on the surface; and the resultant surface is subjected to clearcoating for reinforcing the surface.

[0024] In consideration of kneadability and durability, the amount ofthe pulverized rubber to be incorporated is 1-30 parts by mass,preferably 5-20 parts by mass, on the basis of 100 parts by mass ofrubber components of the aforementioned matrix. When the amount is lessthan one part by mass, the resilience of the resultant ball cannot beeffectively reduced, resulting in failure to reduce the initial velocityof the ball, whereas when the incorporation amount exceeds 30 parts bymass, the pulverized rubber cannot be fed into a rotor of a kneaderduring a kneading process, resulting in considerably poor workability ofkneading.

[0025] When the one-piece ball of the first aspect of the presentinvention is hit by a driver, preferably, the total carrying distance ofthe ball having a reduced initial velocity is about 4-5 m shorter thanthat of a conventional one-piece ball.

[0026] The one-piece ball of the first aspect of the present inventioncan be recycled repeatedly. Furthermore, a conventional one-piece ballexhibiting excellent durability—specifically, in a durability test inwhich the one-piece ball is repeatedly hit by use of a driver at a headspeed of 45 m/s, the ball is not broken until when the ball is hit 1,500times—is pulverized and incorporated into the one-piece ball of thefirst aspect of the present invention, and thus durability of theone-piece ball is lowered by a very small amount. Therefore, accordingto the first aspect of the present invention, recycling of the one-pieceball containing pulverized rubber can be repeated; i.e., pulverizedrubber can be obtained from the one-piece ball repeatedly.

EXAMPLES

[0027] (First Aspect of the Present Invention)

[0028] A commercially available one-piece ball was pulverized by use ofa pulverizer, to thereby produce pulverized rubber. The composition ofthe matrix of the one-piece ball is shown in Table 1. TABLE 1 ComponentAmount (parts by mass) 1,4-Cis-polybutadiene 100 Methacrylic acid 20.0Zinc oxide 23.0 Dicumyl peroxide 1.5

[0029] Subsequently, the resultant pulverized rubber was kneaded intothe matrix of a one-piece ball predominantly containing butadienerubber, to thereby produce a one-piece ball (Examples 1 through 3). InComparative Example 1, a conventional one-piece ball predominantlycontaining butadiene rubber was produced. Table 2 shows the compositionsof the one-piece balls of Examples 1 through 3 and ComparativeExample 1. In each of Examples 1 through 3 and Comparative Example 1,predetermined vulcanization, removal of burrs, and coating were carriedout, to thereby complete formation of a one-piece ball. Thereafter, theresultant one-piece ball was subjected to measurement of outer diameter,weight, hardness, initial velocity, and durability against hitting bymeans of the below-described methods. Kneadability of the pulverizedrubber was evaluated during production of the one-piece ball. Theresults are shown in Table 2.

[0030] Outer Diameter

[0031] The outer diameter of the one-piece ball was measured at 15points by use of a dial gauge.

[0032] Hardness

[0033] The hardness of the one-piece ball was measured at 10-130 kg byuse of a μ hardness meter (N=30).

[0034] Initial Velocity

[0035] The initial velocity of the one-piece ball shot at 1,376 rpm wasmeasured by use of a USGA-type initial velocity meter.

[0036] Durability Against Hitting

[0037] The one-piece ball was repeatedly hit at a head speed of 45 m/sby use of a driver (No. 1 wood) (N=10), to thereby measure the smallestnumber of hits at which the ball began to crack (the number of hits atwhich cracking started), as well as the average number of hits at whichthe ball began to crack (the average number of hits at which crackingstarted).

[0038] Kneadability

[0039] Kneadability of the pulverized rubber was evaluated according tothe following criteria.

[0040] ∘: Good

[0041] Δ: Slightly poor TABLE 2 Comp. Ex. 1 Ex. 2 Ex. 3 Ex. 1Composition 1,4-Cis-polybutadiene 100 100 100 100 (parts by mass)Methacrylic acid 20.0 20.0 20.0 20.0 Zinc oxide 23.0 23.0 23.0 23.0Dicumyl peroxide 1.5 1.5 1.5 1.5 Pulverized rubber 10 20 30 0 ProductOuter diameter (mm) 42.64 42.66 42.66 42.65 Weight (g) 45.57 45.55 45.6245.60 Hardness (mm) 2.67 2.66 2.68 2.66 Initial velocity (m/s) 73.4273.35 73.22 73.50 Durability The number of hits at 1156 1121 1020 1208against which cracking started hitting The average number of 1187 11531130 1251 hits at which cracking started Kneadability O O O˜Δ —

[0042] As is clear from Table 2, the initial velocity of the one-pieceball of the first aspect of the present invention is lower than that ofthe conventional one-piece ball of Comparative Example 1, although theone-piece ball of the first aspect of the present invention is nearlyidentical with the conventional one-piece ball in terms of outerdiameter, weight, and hardness. The results also show that the one-pieceball of the first aspect of the present invention exhibits sufficientdurability to serve as a practice golf ball, although the durabilityagainst hitting becomes slightly poor as the incorporation amount of thepulverized rubber increases. Note: in the case of a typical course ball(game ball), which is not a one-piece ball, the average number of hitsat which cracking starts is about 300.

[0043] (Second Aspect of the Present Invention)

[0044] A commercially available one-piece ball was pulverized by use ofa pulverizer, to thereby produce pulverized rubber. The matrixformulation of the one-piece ball is shown in Table 1.

[0045] Subsequently, the resultant pulverized rubber was kneaded intothe matrix of the core of a two-piece sold golf ball (two-piece ball)predominantly containing butadiene rubber, to thereby produce atwo-piece ball (Examples 4 and 5). In Comparative Example 2, aconventional two-piece ball was produced. Table 3 shows the compositionsof the two-piece balls of Examples 4 and 5 and Comparative Example 2. Ineach of Examples 4 and 5 and Comparative Example 2, predeterminedvulcanization, removal of burrs, cover formation, and coating werecarried out, to thereby complete formation of a two-piece ball.Thereafter, the resultant two-piece ball was subjected to measurement ofouter diameter, weight, hardness, initial velocity, and durabilityagainst hitting by means of the below-described methods. Kneadability ofthe pulverized rubber was evaluated during production of the two-pieceball. The results are shown in Table 3. When the pulverized rubber wasincorporated in an amount of 50 parts by mass on the basis of 100 partsby mass of the rubber component of the matrix of the core, thepulverized rubber could not be satisfactorily fed to a rotor of akneader, resulting in failure to produce a two-piece ball.

[0046] Outer Diameter

[0047] The outer diameter of the two-piece ball was measured at 15points by use of a dial gauge.

[0048] Hardness

[0049] The hardness of the two-piece ball was measured at 10-130 kg byuse of a μ hardness meter (N=30).

[0050] Initial Velocity

[0051] The initial velocity of the two-piece ball shot at 1,376 rpm wasmeasured by use of a USGA-type initial velocity meter.

[0052] Durability Against Hitting

[0053] The two-piece ball was repeatedly hit at a head speed of 45 m/sby use of a driver (No. 1 wood) (N=10), to thereby measure the smallestnumber of hits at which the ball began to crack (the number of hits atwhich cracking started), as well as the average number of hits at whichthe ball began to crack (the average number of hits at which crackingstarted).

[0054] Kneadability

[0055] Kneadability of the pulverized rubber was evaluated according tothe following criteria.

[0056] ∘: Good

[0057] Δ: Slightly poor TABLE 3 Comp. Ex. 4 Ex. 5 Ex. 2 Compo-1,4-Cis-polybutadiene 100 100 100 sition Zinc acrylate 25.0 25.0 25.0 *1Zinc oxide 30.0 30.0 30.0 (parts Aging preventive agent 0.1 0.1 0.1 byDicumyl peroxide 0.6 0.6 0.6 mass) Pulverized rubber 10 30 0 ProductOuter diameter (mm) 42.71 42.71 42.72 Weight (g) 45.16 45.05 45.23Hardness (mm) 3.03 3.23 2.92 Initial velocity (m/s) 77.10 76.90 77.30Durability The number of hits at 342 333 350 against which crackingstarted hitting The average number of hits at which cracking 403 393 412started Kneadability ο ο˜Δ —

[0058] As is clear from Table 3, the initial velocity of the two-pieceball of the second aspect of the present invention decreases as theincorporation amount of the pulverized rubber increases, and the initialvelocity of the two-piece ball is lower than that of the conventionaltwo-piece ball of Comparative Example 2, although the two-piece ball ofthe second aspect of the present invention is nearly identical with theconventional one-piece ball in terms of outer diameter, weight,hardness, and durability. Therefore, the great difference in carryingdistance between a course ball (two-piece ball) and a practice golf ball(one-piece ball) can be reduced to about 3-10 mn.

[0059] The one-piece solid golf ball of the first aspect of the presentinvention has suppressed restitution to thereby attain a reducedcarrying distance and is easily produced, with feeling on impact anddurability being maintained at the level of a conventional one-pieceball. Also, the one-piece solid golf ball is advantageous in that it canbe recycled repeatedly.

[0060] The multi-piece golf ball of the second aspect of the presentinvention has low restitution and thus attains a short carryingdistance, and is suitable for use as a practice golf ball. Specifically,the multi-piece golf ball has the following advantages.

[0061] (1) According to the second aspect of the present invention, whenpulverized rubber is incorporated in an appropriate amount into the coreof a multi-piece golf ball, the resilience of the core is reduced,resulting in reduction of the initial velocity of the ball upon beinghit. As a result, the aforementioned great difference in carryingdistance between a course ball and a practice golf ball, which isestimated to 20-30 m, can be reduced to about 3-10 m.

[0062] (2) A conventional practice one-piece golf ball has induced missshots (i.e., an intended carrying distance of the ball is not obtained)at a golf course, since the trajectory of the one-piece ball differsfrom that of a course ball, by virtue of the difference in spin amountbetween these balls, the difference being attributed to the differencein hardness. However, when the multi-piece golf ball is used for golfpractice, since the trajectory of the ball is similar to that of acourse ball, the aforementioned miss shot can be prevented.

[0063] (3) Since the multi-piece golf ball of the second aspect of thepresent invention contains pulverized rubber, the material cost of theball is reduced. Therefore, even when the multi-piece ball is producedas a practice golf ball, the production cost of the ball is maintainedat a commercially practicable level.

What is claimed is:
 1. A one-piece solid golf ball comprising a matrixcontaining one or more rubber components in which butadiene rubber is apredominant component, and pulverized rubber obtained by pulverizing aone-piece solid golf ball predominantly containing butadiene rubber,wherein the pulverized rubber is incorporated in amount of 1-30 parts bymass on the basis of 100 parts by mass of the rubber components of thematrix.
 2. A one-piece solid golf ball according to claim 1, wherein thebutadiene rubber is 1,4-cis-polybutadiene.
 3. A one-piece solid golfball according to claim 1, wherein the pulverized rubber is incorporatedin an amount of 5-20 parts by mass on the basis of 100 parts by mass ofthe rubber components of the matrix.
 4. A one-piece solid golf ballaccording to claim 1, wherein the pulverized rubber comprises rubberparticles having an average size of more than 0.80 mm and rubberparticles having an average size of 0.80 mm or less, in an amount ofabout 30% and in an amount of about 70%, respectively.
 5. A multi-piecegolf ball comprising a core and one or more cover layers, the corecomprising a matrix and pulverized rubber obtained by pulverizing aone-piece solid golf ball, the matrix containing one or more rubbercomponents, wherein the pulverized rubber is incorporated in an amountof 1-30 parts by mass on the basis of 100 parts by mass of the rubbercomponents of the matrix.
 6. A multi-piece golf ball according to claim5, wherein the matrix of the core predominantly contains butadienerubber, such as 1,4-cis-polybutadiene, which is cross-linked by use of across-linking agent predominantly containing zinc acrylate.
 7. Amulti-piece golf ball according to claim 5, wherein the one-piece solidgolf ball from which the pulverized rubber is obtained predominantlycontains butadiene rubber, such as 1,4-cis-polybutadiene, which iscross-linked by use of a cross-linking agent predominantly containingmethacrylic acid and zinc.
 8. A multi-piece golf ball according to claim5, wherein the pulverized rubber is incorporated in an amount of 5-20parts by mass on the basis of 100 parts by mass of the rubber componentsof the matrix.
 9. A multi-piece golf ball according to claim 5, whereinthe pulverized rubber comprises rubber particles having an average sizeof more than 0.80 mm and rubber particles having an average size of 0.80mm or less, in an amount of about 30% and in an amount of about 70%,respectively.